This disclosure relates to wafer-level cameras, lens plates for wafer-level cameras and methods of manufacturing lens plates for wafer-level cameras.
A wafer-level camera is a camera having a small footprint that is typically utilized in a mobile phone, notebook computer, tablet computer, among others. A wafer-level camera includes optics to form an image and an image sensor for sensing the image. To form a high quality image, the optics of the camera module may include several lenses, stacked on the image sensor and sometimes separated by spacers.
The wafer-level camera is typically manufactured by stacking and bonding wafers with components thereon, utilizing techniques similar to semiconductor manufacturing. For example, a wafer having a plurality of image sensors may be provided first. A spacer wafer may be placed on the image sensor wafer. The spacer wafer has a plurality of openings, each aligned with one of the image sensors. A wafer having a plurality of lenses, known as a lens plate, is then placed on the spacer wafer. The lenses of the lens plate and the openings of the spacer wafer are aligned with the image sensors. A second spacer wafer may be provided before a second lens plate having a plurality of lenses is placed on the wafer stack. In this manner, multiple spacer wafers and multiple lens plates may be included in the manufacturing of wafer-level cameras. Finally, the stacked wafers are diced into individual wafer-level cameras each having an image sensor and a stack of spacers and lenses.
In wafer-level cameras, one or more spacer wafers are typically aligned with a lens plate, and bonded to the lens plate using an epoxy. This is commonly done before lenses are formed on the lens plate. This spacer-to-lens-plate bonding may be difficult, since epoxy must be applied between the spacer wafer and the lens plate, but not in or over any spacer openings. Also, an uneven bond thickness can result in variable spacer thickness.
Conventional spacer wafers for wafer-level cameras are commonly formed of glass wafers, manufactured by drilling holes through the glass wafers. The drilling process can be carried out by laser cutting, abrasive water jet cutting, sandblasting, chemical etching or other processes. Laser drilling is extremely expensive and time consuming; for example, it is not uncommon for 80 percent of the total manufacturing cost of a spacer wafer for a wafer-level camera to be associated with laser drilling. Laser drilling also involves long lead times. If a new array pitch or opening diameter is required, it may take weeks or longer to procure a spacer wafer. This is especially problematic for rapid prototyping of lens designs and development work. Also, in conventional approaches, the possible spacer thicknesses are limited to the available standard glass wafer thicknesses.